Recently, digitalization of audio and visual processing has become wide spread. A DVC (Digital Video Cassette Recorder) for digital recording and reproduction is also being developed. Digitalization prevents noises from entering the into transmission and recording so that the signal quality is improved. In such digital recording, the original can be completely exactly duplicated and it is highly required to protect the copyright of information recorded on recording media.
In particular, provisions for copyright protection of animation images including sound data are being specified by the organizations concerned. They include the VHRA (Video Home Recording Act), which has been proposed in Japan and is currently discussed mainly in the United States. The VHRA specifies that the analog connection using analog devices as sources shall adopt the macro-vision method or CGMS (Copy Generation Management System)-A method, and that the analog connection using digital devices as sources shall adopt the macro-vision method, and that the digital connection using digital devices as sources shall adopt the CGMS-A (Copy Generation Management System--Analog) method or the CGMS-D (Copy Generation Management System--Digital) method.
The macro-vision method used in the analog connection overlays the copy guard signal during the vertical flyback time of the video signal to make normal recording difficult. That is, this method changes the synchronous signal level of the image to make the synchronous detection by a recording device impossible and also changes the burst phase to make the normal color reproduction by a recording device difficult. Thus, the image signal with overlaid copy guard signals prevents normal image recording without any particular procedure by a recording device.
In addition, the CGMS-A method inserts a flag to indicate whether the data can be copied or not in a predetermined horizontal period during the vertical flyback time of the video signal, and the recording device controls its recording according to the flag.
The CGMS-D method used in the digital connection adds a two-bit copy generation management information to the recording format or the digital interface format (data format for transmission) peculiar to devices such as digital VCRs and DVDs. Reproduction devices always insert a copy generation management information into the output signal and recording devices detect the copy generation management information from the input signal to control recording.
The copy generation management information indicates that copying is prohibited with "11", and that copying is allowed only once with "10", and that copying can be made freely with "00". When the copy generation management information contained in the input signal is "10", recording devices record the input signal and change the copy generation management information to "11" (copy prohibition) during recording. This means that the signal cannot be copied again.
For the digital VCR (hereinafter also referred to as DVC), the Consumer Digital VCR Association of Japan established SD (Standard Definition) Standards corresponding to the NTSC or PAL standards and HD (High Definition) Standards corresponding to the high definition TV. These SD and HD standards (hereinafter collectively referred to as DVC standards) already have provisions about the recording format and the digital interface format for the copy generation management information in the DVC. That is, for both of the recording format and the digital interface format, the copy generation management information is inserted in the source control packet in the VAUX area to be described later.
In addition to the DVC standard, it is specified that the copy generation management information will be inserted in the header of the MPEG2 transport stream. However, other standards do not consider CGMS-D, and have no provision for where in the packet or interface format of various digital signals and devices the copy generation management information shall be inserted.
According to the standard currently under discussion by the IEC (International Electrotechnical Committee), a device handling various images will record the copy generation management information in its recording digital data and will output the digital interface output including the copy generation management information in data reproduction. In addition, it is specified that a recording device to record such interface output will detect the copy generation management information and record the data corresponding to it.
Meanwhile, network systems have been recently developing with the progress of multimedia. The multimedia technology requires not only data transmission between personal computers, but also data transmission with audio and video devices (hereinafter referred to as AV devices).
For this purpose, a unified standard of digital interface method for data transmission between a computer and a digital image device is being studied. As a low-cost peripheral interface suitable for multimedia application, IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 1394 is most likely to be adopted.
IEEE 1394 enables multiple data transmission for a plurality of channels. In addition, IEEE 1394 has an isochronous transmission function to ensure transmission of video and sound data in a specified time and is considered to be a digital interface suitable for image transmission.
For IEEE 1394, detailed commands are currently specified in DVB-WG (for European digital broadcasting) of the Digital VCR Association, R4.1 of EIA discussing DTV (Digital TV) decoder in the U.S. and IEEE 1394 T.A. (Trade Association). IEEE 1394 is originally based on computer technologies, but since it is capable of synchronous communication, audio and video equipment manufacturers are also working for standardization. The proposal from the Digital VCR Association is also discussed in 1394 TA.
Detailed contents of IEEE 1394 are described in an article titled "Comparison of Three New Interfaces Searching for the Post-SCSI Design Concept" on pp. 152 to 163 of Nikkei Electronics (No. 612, dated Jul. 4, 1994) (Literature 1). IEEE 1394 is also described in detail in the Japanese Patent Application Laid-open No. Heisei 8-279818.
IEEE 1394 enables multiple transmission for a plurality of channels and achieves transmission of video data from a plurality of devices using a plurality of channels assigned to the isochronous packet. For the digital interface of IEEE 1394, however, no rule about copy protection is specified. According to IEEE 1394, the data in the digital interface format of various device such as DVC transmission format (hereinafter referred to as D-interface format) and MPEG2 transport packet, are just transmitted with format conversion.
Therefore, when data are transmitted using IEEE 1394 to copy an image, the recording device fetches data from the data flowing in the bus of IEEE 1394, and restores the fetched data to the digital interface format peculiar to the reproduction device, and then, extracts the inserted copy generation management information. The copy generation management information is obtained by detecting the insertion position of the copy generation management information with its digital interface processing section or recorded and reproduced data processing sections, such as an error correction circuit. For example, when the transmitted data is DVC data, copying is controlled according to whether the predetermined 2-bit data in the source control packet in VAUX is "11" or "10" or "00".
FIG. 1 is a block diagram showing a device having a digital interface according to IEEE 1394 standard. FIGS. 2 and 3 illustrate the D-interface format and MPEG2 transport stream, respectively.
Reproduction (sending) devices 1 and 2 are DVC and DVD, respectively. These reproduction devices 1, 2 and a recording (receiving) device 3 are connected by a bus 25 corresponding to IEEE 1394 standard. After predetermined processing of signals for the reproduced data with a reproduction processing circuit 4, the reproduction device 1 converts the reproduced data into D-interface format data using a D-interface format output processing circuit 5.
FIG. 2 shows the format of the data from the D-interface format output processing circuit 5. In the D-interface format as the digital VCR standard, data in a single record track of VCR are converted to 150 packets so that the data are transmitted by the unit of 150 packets.
At the head of such 150 packets, a header packet H is laid out. It is followed by two subcode packets SC and three video auxiliary packets VA. Then, nine audio packets A0 to A8 corresponding to nine sync, blocks and 135 video packets V0 to V134 corresponding to 135 sync, blocks. The copy generation management information is inserted in the source control packet in the shaded video auxiliary packet VA. Further, the reproduced data are supplied to a 1394 interface 6, converted to IEEE 1394 packets, and then sent to the bus 25.
The reproduction device 2 processes the signals of the reproduced data using a reproduction processing circuit 7. The data from the reproduction processing circuit 7 is supplied to the MPEG TS output processing circuit 8 and converted to the transport stream according to the MPEG2 standard.
FIG. 3 shows the transport stream. The transport stream supports multiple programs (channels) and can select the packet of the desired program from a plurality of programs transmitted by time sharing in the decoding process. For this selection, the transport stream is transmitted with an additional link level header (shaded part) before the payload for information transmission as shown in FIG. 3. Among 188 bytes of the transport packet, 4 bytes represent the link level header. The copy generation management information is inserted in this header. The transport stream of MPEG2 is converted to IEEE 1394 packets by a 1394 interface 9, and then sent out to the bus 25.
The recording device 3 has a 1394 interface 10, which fetches IEEE 1394 packets in the data from the reproduction devices 1, and 2 flowing in the bus 25, and depackets them. The 1394 interface 10 outputs the depacketed data to the corresponding decoders Specifically, the received data based on the data from the reproduction device 1 are supplied to a D-interface decoder for DVC 11 and the received data based on the data from the reproduction device 2 are supplied to a TS decoder for MPEG2 12. Data of other types are similarly supplied to the corresponding decoders. In FIG. 1, decoders corresponding to other types of data are represented by a D-interface decoder for other data 13.
The decoders 11, 12, 13 decode the input data. The decoding results are supplied to a format converting circuit 17 via flag detecting circuits 14, 15, and 16. The format converting circuit 17 converts the input data to the data in its own recording format and supplies them to a recording processing circuit 18.
The flag detecting circuits 14, 15, and 16 detect the copy generation management information in the output from the decoders 11, 12, 13, respectively, and output the information to a recording controlling circuit 19. The recording controlling circuit 19 controls recording (copying) by the recording processing circuit 18 according to the detected copy generation management information.
IEEE 1394 allows connection a maximum of 63 notes to the bus 25. For the copy generation management information, the recording device is required to be capable of recognizing and detecting the digital interface format peculiar to the received data. In other words, when several types of data are received and recorded, the recording device is required to support all types of received data, which results in increase of its circuit scale. This further means that it can support the digital interface formats for which the standards have been already set, but cannot support digital interface formats having no set standards yet.
It is also possible to copy the video data with a data streamer, which does not have any image decoding circuit and only records the video data. At present, such a data streamer is not considered as the subject to which the copy generation management information rule is applied, but it may be subject to restriction in the future. However, as described above, a decoder corresponding to various received data is required to detect the copy generation management information from the data received via the bus of IEEE 1394. Even a data streamer, which originally does not need any decoder, may require a decoding circuit for detection of the copy generation management information only.
Since IEEE 1394 allows connection of 63 nodes to a bus, it is possible to make 63 copies at a time. Such copying is allowed under the current rule, but cannot be overlooked from the viewpoint of copyright protection.
Thus, it is an object of the present invention to provide a device having a digital interface which can support any format other than existing ones and can reduce the circuit scale by enabling recording based on the copy generation management information regardless of the format used in the data recorded by the recording device, and to provide a network system and a copy protection method using such a device.
It is another object of the present invention to provide a device having a digital interface which can eliminate the need of a decoding circuit even when the recording device records data according to the copy generation management information, and to provide a network system and a copy protection method using such a device.
It is yet another object of the present invention to provide a device having a digital interface which can enable reproduction of a single copy or a predetermined number of copies only at a time even when a plurality of nodes can be connected and to provide a network system and a copy protection method using such a device.
It is still another object of the present invention to provide a device having a digital interface which can execute the copy generation management based on the copy control information without any problem, even when the types of the digital video devices connected to IEEE 1394 increase or a new digital video device with a new digital interface format is connected to IEEE 1394 and to provide a network system and a copy protection method using such a device.